1. Field of the Invention
The present invention relates to fluid pressure mechanism for applying a pulling force and to lift apparatus powered by such mechanism.
2. Prior Art
In a known simple jack, an operating cylinder has an internal piston moved lengthwise of the cylinder by introduction of fluid under pressure. A rigid plunger has an inner end connected to the piston and an outer free end portion extending axially through an end of the cylinder. Such a jack requires a large space for the range of motion to be achieved. In a representative installation, the space in which the jack is mounted must accommodate the entire length of the cylinder plus the desired range of motion of the plunger which, at most, would be approximately equal to the length of the cylinder. Consequently, the most compact installation must provide space for at least twice the desired length of linear motion of the plunger if the simple known fluid pressure jack is used.
With respect to another aspect of the present invention, there are known hydraulically powered lifts some of which have been adapted for underwater installation to raise and lower a large boat or a seaplane, for example. There is no known inexpensive compact lift specially adapted to be mounted on or adjacent to a dock for conveniently raising and lowering a small watercraft such as a skiff, rowboat, canoe or jet ski.